Koji has been utilized as enzyme sources in production of fermented foods and drinks since a long time ago. As koji for producing fermented foods and drinks, there has been conventionally used the solid koji which is obtained by growing koji molds on the surface of cereals and the like. The solid koji is obtained by a traditional production method. However, the method is a special culture mode, that is, solid culture, so unsuitable for large-scale production.
On the other hand, the liquid koji, which is a culture product of koji molds obtained by liquid culturing koji molds, can control culture easily, and a suitable culture mode for efficient production.
However, it is well known that the liquid koji mold does not provide sufficient enzyme activity required for producing fermented foods and drinks, so there are few examples in which the liquid koji is used for actual production (see, Non-patent Documents 1 to 4).
Koji molds easily proliferate, media therefore may be prepared at low cost, and no special culture apparatuses are required, so the cost for culturing is low. The koji molds have been utilized for producing fermented foods and drinks since a long time ago, so are recognized as a safe host. Thus, it has conventionally attempted to incorporate a gene derived from koji molds or from the other organisms by using the koji molds as host to strongly express the genes, to thereby produce products derived from the genes, that is, recombinant proteins (see, Non-patent Document 5).
There also has been reported a successful example of producing recombinant protein in high yields by solid culture with wheat bran (see, Non-patent Document 6). However, the production was performed in a special culture mode, that is, solid culture, so unsuitable for large-scale production.
On the other hand, it has been thought that the liquid culture inherently provides few proteins outside cells as described above, and thus is unsuitable for mass-production of recombinant protein.
Non-patent Document 1: Hata Y. et al.: J. Ferment. Bioeng., 84, 532-537 (1997)
Non-patent Document 2: Hata Y. et al.: Gene, 207, 127-134 (1998)
Non-patent Document 3: Ishida H. et al.: J. Ferment. Bioeng., 86, 301-307 (1998)
Non-patent Document 4: Ishida H. et al.: Curr. Genet., 37, 373-379 (2000)
Non-patent Document 5: R. J. Gouka, et al., Appl. Microbiol. Biotechnol., 47, 1-11 (1997)
Non-patent Document 6: K. Tsuchiya, et al., Biosci. Biotech. Biochem., 58, 895-899 (1994)